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Times are changing in the building controls sector. Direct digital control has been prevalent in the sophisticated controllers used in Building Management Systems (BMS) for the last 20 years. Now, advances in electronics design and development are enabling manufacturers to bring the advantages of digital technology to simpler field devices. Terry Sharp, Sales and Marketing Director of Sontay tells us more.
Driven by the availability of emerging, low-cost technologies, digital control is rapidly becoming more widespread in the BMS sector. It is, in fact, cascading down the tiers of equipment commonly in use, from complex programmable outstations through application specific field controllers and time-clocks to more humble, field-based devices which feature in a typical BMS. This digitisation process is bringing key benefits to the consultants, contractors and controls specialists designing and engineering these systems, and ultimately is capable of rewarding the building occupants too.
Small is beautiful, so the saying goes, and in the controls industry size is definitely an issue. Thanks to continuing improvements in electronic product design, devices using digital electronics can be assembled using smaller components than analogue field devices. All the electronics are shrunk into a single custom-built chip. These integrated circuits means that field devices can now be manufactured much smaller than equivalent analogue equipment. Indeed, one same size product can now be a home for multiple controllers. Industry-standard product housings can therefore offer greater functionality whilst custom-designed controllers can be developed much smaller than was previously possible, and either embedded within the controlled process or installed as a plant device within the control system.
Reliability is another factor. Since electronic controls came into being, manufacturers have been forced to insist on screening and segregated cabling to reduce the noise and interference caused by induced pick-up in the building. Greater reliability is achieved through the ability of the digital electronics to filter out the chaff from cable runs, and the facility to configure these devices to see only the appropriate data. The latest controllers for air handling unit electric heater battery applications on the market are a prime example, these feature burst-power firing techniques to minimise electrical noise and RFI disturbance and avoid the need for additional filtering.
Price is always an important factor in the building services industry. In the past, this has been a barrier to the adoption of digital technology in field-based devices. Analogue products were cheaper, commodity items. Again, thanks to developments in electronics design and the economies of scale brought by mass manufacturing, digital devices offer not only greater functionality but a viable price alternative to their analogue equivalents. There are hidden cost benefits too which should be taken into account. Systems integrators can reduce their engineering and commissioning time and cost by using digital field devices, since they are easier to set up and install.
On-going performance and lower maintenance costs are another key driver behind the growth in popularity of digital field devices. Take the conventional I/O module as an example. In days gone by, these analogue control modules required manual setting and adjustment to off-set voltage drops and component ageing. Only through commissioning and regular maintenance could accurate and efficient operation be assured, resulting in control engineers spending a considerable amount of time twiddling and adjusting calibration knobs to offset these inevitable inaccuracies. Today, modern digital electronics automatically ensure precise and accurate control without the need for frequent adjustment, thereby simplifying the whole calibration task and reducing maintenance to a simple, routine system check. Because digital devices are often configured and calibrated at the factory, the installer can just ‘plug and play’, saving yet more valuable time in the field. On-board LED indication gives the engineer the reassurance of system operating status and allows quick diagnosis of system faults, wiring errors or malfunction.
Sontay’s latest range of digital I/O controls modules offer convincing proof of these advantages. These devices are capable of carrying out a broad range of HVAC control functions, including alarm integration, step control, binary output driving, multiplexing and raising/lowering of control from a range of control signals. The use of field selectable configuration allows maximum simplicity, efficiency and accuracy in set up, commissioning and performance and offers a wide range of control options from the fewest number of devices. From a manufacturer’s point of view, this new breed of device also helps us serve our customers better, since we end up stocking fewer parts, minimising delays in assembly and delivery.
Self-calibrating digital techniques are not just good news in installation, set-up and maintenance but they will also ensure much more accurate performance over time than their analogue counterparts. Digital chips provide automatic compensation for non-linearity whilst the high quality, digital circuitry and resolution at component level bring unrivalled precision in operation. Quite simply, digital field devices result in a total, precise, repeatable output leading to energy savings through a better performing control system.
Other new types of device, such as relative humidity sensors, also benefit from these higher standards of accuracy. Digital sensors provide reduced hysteresis and repeatability of control signal, features further enhanced by the digital electronics being scaleable, allowing the operating range to be selected. Analogue humidity sensors are not usually adjustable, with 10 volts traditionally being divided by 100 percent of the RH scale. Digital sensors have adjustable sensitivity, so narrowing the range to the preferred RH can result in greater accuracy and higher resolution, important in many of today’s close control applications.
Another advantage is that digital field devices feature the integral ability for two way communication, something that was impossible with analogue products. This two way communication means that control may be more effectively distributed to the field based device and could, in fact, lead to the elimination of an additional dedicated controller upstream elsewhere in the system. If the system was made of intelligent, communicating field devices, why would you need a controller? Ultimately, this works to reduce the complexity and cost of the BMS installation further and paves the way for other emerging technologies, such as wireless communications at the control field level. As a general point, the intelligence built-in to these digital devices makes it much easier for these products to handle data over various communications networks.
These improvements beg the question, what future is there for BMS outstations now that digital technology has arrived at the field level? Traditionally, information is collated and processed by these outstations, but with two way communication feasible directly from digital peripheral devices, then what value do these controllers have? IP addressable field devices using distributed intelligence and wireless communication would appear to be an option for the future.
It seems foolish to put at risk the performance of a BMS on out-dated technology when there is a digital alternative that is so superior. Where now is the advantage in buying analogue? With prices for digital devices on a par with their analogue equivalent, and offering a host of additional features, there’s no question as to the sensible choice. By using digital electronics, Sontay are ensuring that devices are ready for the next generation of communicating devices and are therefore future proof.
